Recent studies have provided considerable support for the concept that type I fibrocytes in the spiral ligament participate actively in cochlear ion homeostasis as part of a pathway for recycling K+ from perilymph to endolymph. If true, then type I fibrocytes should have evolved complex and possibly unique mechanisms for regulating cellular and intercellular K+ flux. Moreover, it is highly probable that these transport processes are under the control of local and systemic modulators. It is planned to test these hypotheses via two Specific Aims. Aim I will identify and characterize specific channels and channel subtypes responsible for regulating the influx and efflux of K+ in cultured and freshly isolated type I fibrocytes with patch clamp recording. Pharmacological tools will be used to identify the specific channel types. Aim 2 will assess the potential role of vasopressin and ATP as systemic and local modulators for regulating K+ homeostasis in type I fibrocytes under normal physiological conditions. Dose-dependent responses to various agonists and antagonists will be fully characterized by patch clamp techniques. Specific pharmacological tools will be utilized to distinguish the receptor types and possible mechanisms involved. Reverse transcription - polymerase chain reaction analysis will be performed to confirm the expression of genes for ion channels identified in Aim I and receptor subtypes defined in Aim 2. Data from this highly focused study will help to verify a portion of the proposed pathway for K+ recycling in our current model of ion homeostasis in the cochlea and thereby provide new insights into potential treatments for hearing impairment.